1. Technical Field of the Invention
This invention relates to manufacturing carbon based materials and, more particularly, to a method and system for net shape manufacturing using carbon nanotubes.
2. Background of the Invention
In addition to the more common allotropes of carbon, namely diamond and graphite, there exist a third form which forms a network of structures called fullerenes. The best known, discovered in 1985, is called the Buckyball or to give its technical name Buckminsterfullerene. A Buckyball structure is a pure carbon molecule comprising exactly sixty carbon atoms. Generally, each carbon atom is bonded to three other carbon atoms in the form of a spherical structure. Recent research has identified another type of fullerene which appears as a hollow tubular structure known as the nanotube. The carbon nanotube appears as an elongated fiber and yet it is hollow and inherits the perfection of atomic arrangements made famous by its predecessor the Buckyball. Carbon nanotubes consist of two dimensional hexagonal sheets folded together and capped at both ends by a fullerene cap. There length can be millions of times greater than their small diameter. Thus, carbon nanotubes are effectively Buckyball structures extended out as long strands rather than spheres.
Development of carbon molecular growth began with the manufacture of carbon fibers and, while these conventional carbon fibers are readily made very long, the graphite sheets within the carbon fibers are either not closed tubes or do not extend continuously along the length of the fiber. The result is sharply decreased tensile strength, electrical conductivity and chemical resistance compared to a carbon nanotube. Thus, development of fullerenes, such as carbon nanotubes, has continued in an effort to develop materials with improved physical properties.
Carbon nanotubes exhibit mechanical, electronic and magnetic properties which are in tuneable by varying the diameter, number of concentric shelves and orientation of the fibers. Practical carbon nanotube based materials require eliminating defects and other reaction products, maximizing the nanotube yield, and synthetically controlling the tube length and orientation. Currently there exist three primary methods for producing carbon nanotubes. These methods include, for example, Electric Arc Discharge, Resistive Heating and Laser Ablation.
The Electric Arc Discharge process works by utilizing two carbon (graphite) electrodes in an arc welding type process. The welder is turned on and the rod ends are held against each other in an argon atmosphere to produce or grow carbon nanotubes. The yield rate of carbon nanotubes of this process is extremely low and the growth of the carbon nanotube orientation are random in nature delivering only undefined configurations of growth material.
In Resistive Heating type processes, the fullerenes are formed when a carbon rod or carbon containing gas is dissociated by resistive heating under a controlled atmosphere. A resisted heating of the rod causes the rod to emit a faint gray white plum soot like material comprising fullerenes. The fullerenes collect on glass shields that surround the carbon rod and must be separated from non-desirable components in a subsequent process. Again, the yield rate of the carbon nanotubes is extremely low and orientation is random delivering only undefined configurations of growth material.
The Laser Ablation batch type process works by ablating a graphite target containing a small metal particle concentration with a pulsed laser while providing a temperature controlled space for the carbon atoms and carbon vapor to combine to grow a fullerene structure such as a nanotube. The fullerene structure falls out in a type of carbon soot. The desired fullerene structure is subsequently extracted from the soot by an acid reflux cleaning system. Although the Laser Ablation process has experienced an improved yield rate, relative to the above-mentioned processes, this batch type process approach is uneconomical for use in industrial application because there currently exist no method for controlling the orientation and shaping of the carbon nanotubes. None of the above-mentioned batch methods are used to delivered large-scale production of carbon nanotubes or crystalline type carbon nanotubes with a defined orientation in a net shape type manufacturing arrangement.
The above-mentioned and other disadvantages of the prior art are overcome by the present invention, for example, by providing a method and system for net shape manufacturing using carbon nanotubes.
The present invention achieves technical advantages as a method and system for net shaped manufacturing using carbon nanotubes. An automatic control unit is used to place reaction units in the proper location to produce a component part of carbon nanotubes in a predetermined shape. The reaction units include a carbon vaporization unit, a carbon and catalyst feed/injection unit and a gas pressure/temperature control isolation unit. The carbon /catalyst feed/injection unit advantageously operates to inject carbon based materials (e.g., graphite powder, solid graphite or carbon based gas) into an reaction area at a predetermined rate in which the carbon vaporization unit provides energy capable of dissociating carbon atoms from the injected carbon based material to produce a predetermined concentration of carbon vapor within the reaction area. The gas pressure/temperature control isolation unit operates to control the pressure and temperature of the reaction area to promote the growth of carbon nanotubes.
Among the new advantages of the present invention are: First, preferentially oriented carbon nanotubes can more economically be fabricated into component parts; And, since preferentially oriented carbon nanotubes exhibit both superior strength and electrical conductivity, stronger structural materials can be fabricated into a component which utilizes both structural advantages and electronic applications.